Topband: RDF

[Bill Tippett]

N4ZR wrote:
 >I have been hunting for more information on RDF

         It is available using EZNEC 3.0 which calculates
Average Gain over the entire 3D pattern.  When choosing
3D Plot, "Average Gain" appears in the box at the bottom of
the summary screen as "Average Gain = -15.77 dB". You then
take  max forward gain (from either Elevation or Azimuth plots)
and subtract Average Gain to get RDF.  In this example, max
forward Gain was -1.81 dB, making RDF = -1.81 - (-15.77)
  = 13.96 dB, so it's the ratio (or arithmetic difference in dB) of gain
in all directions versus gain in the desired direction.  See here
for a summary:

http://www.w8ji.com/receiving.htm

         RDF is better than nothing, but it essentially assumes
equal distribution of noise from all elevations and azimuths.
If you have an idea of the most likely azimuth and elevation
for noise (e.g. where thunderstorms typically are found from
your location), I feel you can get a better idea of array performance
by looking at the actual Az and El plots.  Two arrays could have
identical RDF's, but be quite different depending on the source of
the noise.  For example, one array might achieve its RDF by
compressing the forward beamwidth but another might have an
identical RDF by having very high F/R.  If the noise was from
the backside, the latter would probably be the most effective.

                                 73,  Bill  W4ZV